(DSA) Digital subtraction angiography is a radiographic imaging technique to visualize the blood vessels in the human body. DSA images are produced by the (computer) subtraction of pre-contrast images (the mask) from images after introduction of a contrast medium. Subtracting background structures and enhancing the contrast provides the visualization of blood vessels in a bony or dense soft tissue environment. The images are produced in real time, as the contrast agent is injected into the blood vessels.

Dosage is an important factor in the use of ionization radiation as well as in application of contrast agents or radiopharmaceuticals and the dosage should be comply with the ALARA principle (As Low As Reasonably Achievable).
Ionizing radiation comes from natural and artificial sources. Radiation effects depend on the type of radiation, and various units are used for measurement of dosages including gray, sievert, radiation absorbed dose (RAD), roentgen equivalent in man (REM), and roentgen. The amount of radiopharmaceutical given to a patient is measured in becquerels (Bq).
The dosage of contrast media in radiographic or computer-tomographic procedures should be tailored according to the diagnostic indications, the iodine concentration, and the patient's body size and age.

See also Administrative Dose Guidelines.

A double contrast exam uses both a radiopaque and a radiolucent contrast agent. Double contrast is for example used in gastrointestinal examinations to show the pattern of mucosal ridges. The walls of the intestine are coated with the radiopaque barium and the lumen is filled with radiolucent air.

E-Z-CAT Dry is a dry CT barium contrast powder for suspension and can be mixed and self-administered at home. This may improve examination throughput, reduces patient waiting time and help to minimize waiting room congestion. The light E-Z-Cat® Dry foil packets can also be mailed to patients in remote locations.
The oral contrast agent is well compatible with new scanner technologies and provides a fast transit time through the GI tract.

E-Z-EM, Inc. is headquartered in New York and develops, manufactures and markets diagnostic imaging products.
The business of E-Z-EM encompasses CT imaging, virtual colonoscopy, gastro devices and accessories, and healthcare decontaminants. E-Z-EM is also a third-party contract manufacturer of contrast media. The company provides contract manufacturing services in various product areas, including pharmaceuticals, and cosmetics, as well as the marketing of radiological medical devices, such as entry biopsy needles and mammography wipes and related accessories.
Bracco Diagnostics, Inc. , the US-based subsidiary of Bracco Imaging S.p.A. and part of the Bracco Group, announced in Oct. 2007 that it has entered into a merger agreement to acquire E-Z-EM, Inc. (NASDAQ: EZEM) for a total consideration of about $ 240 million . Upon completion of the procedure and subject to the approval of the regulatory authorities, Bracco Diagnostics Inc. will incorporate E-Z-EM.